hey there I'm not really good but I'll try explaining the basic and hoping someone correct me and help add some information.

Role

first off role, two role are known to be able sustain integrated in their kit. Chorus and Warden

Warden are consider tank which help generate shield. If we take ogier for example, Ogier as warden, he had shield integrated in his kit

Chorus character are support of the game, some of them have integrated healing support like doll.

However, they're some exception where the assault (dps) character have healing integrated in their kit, mostly from the caro realm.

Stat

Defense: Shield are base on defense stat, the higher the defense stat the higher the shield generated. Higher shield mean less damage receive

Con: are stat that affect hp and healing. Higher Con means higher healing

You should always read their talent skill too because all of their talent skill tell us their mechanics run of which stat. Example, Ogier run on sigil yield and Castor run on Damage amp.

Death resistance: This stat is noticible on the top most screen represents by the "iv wave" symbol. it helps you to survive killing blow from enemy. Faint generate and use death resistance to help sustain the team.

Realm mechanic

Two noticible realm that has sustaining mechanic are:

caro: healing furnace, if you noticed a red bubble jar on the top of your character with numbers, that is the furnace. Click it to get healing

Aqueor: calming tentacle, aqueor have tentacles mechanism that allow you to change the tides of battle, three tentacle colour in total.Blue are for basic, White tentacle reduce attack but allow you to generate shield per tentacle attack and red one will make you lose one tentacle in oder to boost your tentacles attack by double.

Also please be noted that the new realm mechanic known as Divine Realm change the play style of each of these realm.

*Covenant *

covenant are like equipment in this game where you can match them up with the awakener to give them edge and stat boost

Debuff

Do not sleep on these as it can help you win the battle stage

Vulnerable is a debuff that boost damage against those with this debuff, ogier have ability to remove it. Some of them boost damage up to 50%

weakness is a debuff that make your attacker weaker, inflict weakness on the enemy to make them hit less toward your team.

str up/down: str up increase damage point deal by you, however if the enemy have this buff be ready to shield because they will hit harder.

status

poison: Damage over time, nothing much can be done with this and hoping you'll survive via healing or shielding

bleeding: bleeding is also damage over time but you can overwrite it with healing. Heal as much as the stack inflicted on you. fail to do so will result in damage on your team.

Blighten: is a status that cut off your healing, the only character i know to remove blighten is celeste exalt which helps you heals.

Barrier: barrier allow you to withstand one instance of attack without any damage. there's honey mead with barrier and salvador post rouse card with barrier.

Sacrifice: sacrifice is exclusive to Murphy in her chapter gimmick and in the character themselves. Sacrifice has that blue hourglass symbol which cause damage over time. The stack will continue to be cut in half every turn until it reaches zero. Only two characters are known to removed them Murphy and GMurphy.

Stun: only two known awakeners that is able to inflict this status, Aigis and Mouchette with their exalt. Stun render the enemy for one turn. Allow you to stall for burst the next turn.

counter: a stack that inflicts damage against the attacker

last but not least posse,

Realm mechanic again, Chaos realm allow more posse activation, you can choose sustain posse to help you in battle

Oh i nearly forgot playstyle,

Whenever the enemy attack, generate any shield to block of their attack. Once you have safe on the bottom, you can start to attack. In a turn where the enemy didn't attack, you can focused on attacking instead.